Among semiconductor integrated circuit devices, particularly in super LSI devices, delay of signals passing through wirings prepared in devices gives rise to a significant problem along with lowering of power consumption as the wirings become finer and are more integrated. Particularly, in a high speed logic device, RC delay due to the resistance and the distribution capacity of wirings results in most prominent subject and, among all it is necessary to use a material of low dielectric constant for inter-wiring insulating materials in order to decrease the distribution capacity.
Heretofore, as an insulating film in a semiconductor integrated circuit, a silica film (SiO2), a tantalum oxide film (Ta2O5), an aluminum oxide film (Al2O3), a nitride film (Si3N4) and the like have been used and, particularly, as an insulating material between multilayer willing, a nitride film and a silica film doped with an organic material or fluorine have been used or studied as the low dielectric constant film. Further, as an insulating film for further lowering the dielectric constant, a fluororesin, a silica film formed by baking a foaming organic silica film, a porous silica film formed by depositing fine silica particles, etc. have been studied.
On the other hand, since diamond is more excellent in the heat conductivity and the mechanical strength than other materials, this is a material suitable to heat dissipation for semiconductor devices of high integration degree and large heat generation amount and has been studied in recent years. For example, JP-A No. 6-97671 proposes a diamond film of 5 μm thickness by a film forming method such as a sputtering method, ion plating method or duster ion beam method. Further, JP-A No. 9-263488 proposes a film forming method of scattering fine diamond particles on a substrate and growing diamond crystals using them as nuclei by supplying carbon by a CVD (Chemical Vapor Deposition) method.
The present inventors have obtained a specific dielectric constant of 2.72 by a fine diamond particle film of a porous structure as already disclosed in JP-A No. 2002-110870. Further, since fine diamond particles do not bond to each other, this results in a problem that the film strength is lowered and, in order to solve the problem, JP-A No. 2002-289604 proposes a reinforcing method by crosslinking fine diamond particles by means of a hexachlorodisiloxane treatment and it is shown that a specific dielectric constant comparable with that in JP-A No. 2002-110870 is obtained also by the treatment.
Further, the present inventors have reported that a specific dielectric constant of 2.1 is obtained by heating and purifying fine diamond particles in a mixed acid comprising sulfuric acid/nitric acid in the Academic Conference (The 50th meeting of the Japan Society of Applied Physics and Related Societies, Pre-text No. 2, p 913 (2003)).
Materials known so far as having low dielectric constant are listed in the following table.
TABLE 1Name of materialSpecific dielectric constantSilica (plasma CVD)4.2-5.0Fluorine-added silica3.7Diamond (single crystal)5.68Porous silica1.5-2.5Porous diamond 2.1-2.72Polyimide3.0-3.5Polytetrafluoroethylene1.9Gas1Patent Document 1: JP-A No. 6-97671Patent Document 2: JP-A No. 9-263488Patent Document 3: JP-A No. 2002-110870Patent Document 4: JP-A No. 2002-289604Non-Patent Document 1: The 50th meeting of the Japan Society of Applied Physics and Related Societies, Pre-text No. 2, p 913 (2003).